To predict the response of patients with rheumatoid arthritis (RA) to infliximab, patient profile and laboratory findings were compared to determine whether there was any association with the clinical course of the disease, and the clinical significance of serum rheumatoid factor (RF) in the response to this treatment was considered. Sixty-two RA patients were treated with infliximab, 87.9% of whom were positive for RF. At baseline and 12 months after the start of treatment, RF titers were significantly lower in the low-CRP group (CRP at 12 months<0.3 mg/dl) compared with that in the high-CRP group (CRP at 12 months >1.5 mg/dl). Furthermore, at baseline and 12 months, RF titers were significantly lower in the good-CRP-response group (DeltaCRP>or=1.5 mg/d) compared with the poor-CRP-response group (DeltaCRP<or=0.3 mg/d). The percent changes in RF and CRP from baseline were correlated throughout the clinical course. The duration of disease in good-CRP-response group was shorter than that in poor-CRP-response group significantly. The rate of positivity for HLA-DR4 in good response group tends to be higher than that in poor-CRP-response group. We concluded that several factors, including disease duration, positivity for HLA-DR4, and the serum RF titer at baseline, might predict the patient response to infliximab.